EP0074755B1 - Process for the reclamation of foundry sands - Google Patents
Process for the reclamation of foundry sands Download PDFInfo
- Publication number
- EP0074755B1 EP0074755B1 EP82304595A EP82304595A EP0074755B1 EP 0074755 B1 EP0074755 B1 EP 0074755B1 EP 82304595 A EP82304595 A EP 82304595A EP 82304595 A EP82304595 A EP 82304595A EP 0074755 B1 EP0074755 B1 EP 0074755B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- sand
- energy
- binder
- reclamation
- fluid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C5/00—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose
- B22C5/10—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose by dust separating
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Mold Materials And Core Materials (AREA)
- Disintegrating Or Milling (AREA)
Description
- This invention concerns the reclamation of foundry sands.
- Foundry sand is used with suitable binding agents for making moulds and cores for casting metal. Various binders, both inorganic and organic, are used to bond the foundry sand and, for many years, the sand after use was discarded.
- In an attempt to reduce the running costs of foundries and to reduce environmental pollution, various processes have been suggested in an attempt to enable the foundry to re-use sand, preferably many times over. Problems have always arisen in that the amount of binder to be removed from the used foundry sand to enable it to be re-used is quite critical and, hitherto, it has only been possible to use again some reclaimed sand together with some fresh sand if satisfactory binding is to be achieved and suitable moulds and cores made.
- A paper entitled "Trends in Sand Reclamation" was given at the British Cast Iron Research Association International Conference in 1979, by Mr. D. A. Taylor and in this paper reference is made to water washing and attrition, which can be carried out by various means including crusher units, vibrators, pneumatic impellers and shot blasting. For organic binders incineration has also been proposed. In relation to silicate bonded sands, it is suggested that only intensive attrition and/or water washing can remove sufficient sodium oxide to allow re-use of the sand.
- British Patent Specification No. 1,322,864 is also concerned with the problem of sand reclamation and discloses a process in which the used foundry sand is introduced into a blast of fluid under pressure, whereby the sand is projected against lateral walls of a hermetically sealed casing to cause a matrix of the binding agent to burst releasing the sand. The product of this process is then subjected to granulometric selection to remove the fines generated by the high impact.
- British Patent Specification No. 1,505,904 discloses a process in which coated sand particles are projected in a current of gas against the interior surface of a rotating drum.
- British Patent Specification No. 2,019,274 discloses a similar process in which, again, the coated sand is projected against a. solid target.
- Other reclamation methods have been disclosed in, for example, British Patent Specification No. 1,593,008, in which used foundry sand is suspended in a fluidised bed and subjected to jets of compressed air whilst in the fluidised state. Japanese Patent Specification No. 51109941, published on 3 April 1978, concerns a similar method in which fluidised sand is subjected to abrasion by stirrer blades rotated at high speed inside the fluidised bed of sand.
- US Patent No 2 478 461 also discloses a process for the removal of binder from foundry sand, but appears to be mainly concerned with binders which generate a carbonaceous residue. It is suggested that this residue can be burned and the partially cleaned sand further cleaned by subjecting high velocity sand grains issuing from nozzles to severe erosive action and further suggests the provision of an abrasive-resistant lining (18). This specification, like other referred to earlier in which targets are specified, may well introduce contaminants from the target into the sand.
- The essential problem to be overcome in the sand reclamation process is an adequate balancing of two objectives, namely the effective removal of a hard and tenacious coating and the avoidance of significant particle degradation of the clean sand particles to produce fines which are not useful in the reclaimed sand. The present invention provides a process which effectively balances these two objectives.
- Experiments have shown that it is acceptable to have up to a total of 0.8% by weight of soda on sand, including the fresh silicate binder, when reclaimed sand is reused in foundry core work, without having to add fresh uncontaminated sand to the core mixture. This is equivalent to the removal of 65-70% of the soda coated onto the sand in the normal carbon dioxide or ester silicate processes.
- If less soda is removed a proportion of fresh sand needs to be included to ensure the production of satisfactory cores and moulds. Such removal can be obtained when organic binders are removed from' foundry sand by attrition or incineration, but no satisfactory method has hitherto been proposed for the removal of silicate binder to this extent, without causing significant disintegration of the sand, so producing useless fines which merely contaminate the system.
- Experiments involving increased fluid energy input into a fluidised bed system have proved unsatisfactory in that the additional energy destabilises the fluidised bed container carrying the fluidised bed.
- Accordingly, the present invention provides a process for the reclamation of silicate binder coated foundry sand, in which the coated foundry sand is subjected to a fluid energy acceleration to remove the binder and the reclaimed sand is separated from the binder debris, characterised in that the fluid energy is imparted to the sand in a fluid energy mill to a sufficient extent to substantially remove the binder coating without causing significant disintegration of the sand particles and in which the energy imparted to the sand is less than 1,300 kilojoules per kilogramme of coated sand and in which the Reynolds Number arising from the energy-imparting jet stream does not exceed 6.5x104.
- In the equipment used for this work, the optimal energy range was from 400 to 1,200 kilojoules per kilogramme of sand. This work was carried out in a microniser having a diameter of 10 cm and containing six 1.6 mm diameter inlet nozzles in the periphery of the chamber. The feed rate of the sand varied from 0.33 to 1.54 per second and the optimum feed rate was of the order of 1 g per second for this apparatus.
- Using a commercial production size of fluid energy mill-or microniser the sand feed rate can be increased in relation to the size of the mill and air throughput. The specific energy imparted to the sand should be of the same order of magnitude as previously defined but applied at a commercially useful sand feed rate.
- Fluid energy or jet mills (alternatively known as Micronisers) suitable for use in the process of this invention are available from various suppliers in the market and are described in, for example, Chemical Engineering Handbook, Ed. J. H. Perry, 4th ed., McGraw Hill, p. 8-42 and 43. Such mills consist essentially of a chamber in which the contaminated sand is acted upon by a number of gaseous fluid jets issuing through orifices spaced around the periphery of the substantially circular chamber.
-
- E=Energy due to expansion (kw)
- R=Universal Gas Constant (8.314 kJ/k mol °K)
- T=Absolute Temperature (°K)
- W=molal flowrate (k mol/s)
- P1-=Absolute air pressure applied to nozzles (N/m2)
- Po=Absolute air pressure after expansion (N/m2) assumed to be atmospheric pressure y=ratio of specific heats (CP/CR).
-
- It will be appreciated that the imparted energy figures set out above relate to a specific piece of apparatus, but it is thought that by simple experiment the work can readily be applied to other types of fluid' energy mill. To assist in this generalisation and to relate the forces involved to the fluid input stream, Reynolds Number calculations have been carried out.
- Reynolds Number is the ratio of inertial force to the viscous force of the flowing fluid. It is a measure of the air fluid velocity in the jet stream which determines the drag force exerted on the individual particles and thus determines their acceleration and their impact velocity. Reynolds Number can be calculated on the basis of the fluid mass flowrate through a single nozzle (Qf) of nozzle diameter, d",
- In general, it is preferred that the Reynolds Number is in the range 4.Ox104 to 6.4x104.
- Using the 10 cm diameter microniser referred to earlier, a sample of foundry sand which had previously been used in a silicate bonded core was treated in accordance with the invention and the results are set out below.
-
- It can be seen from the Examples that in the preferred range of specific energy and Reynolds number mode of operation of the process of this invention, that more than 60% of the soda on used sand can be removed whilst fines are less than 15%.
- If higher energies are used, although even more soda is removed, unacceptably large quantities of fines are produced-see Exp. 1.
- As mentioned earlier, if sufficient soda is removed, sand can be reused without any addition of fresh sand, so giving a valuable benefit to the user.
Claims (3)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8126689 | 1981-09-03 | ||
GB8126689 | 1981-09-03 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0074755A1 EP0074755A1 (en) | 1983-03-23 |
EP0074755B1 true EP0074755B1 (en) | 1986-01-15 |
Family
ID=10524292
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP82304595A Expired EP0074755B1 (en) | 1981-09-03 | 1982-09-01 | Process for the reclamation of foundry sands |
Country Status (8)
Country | Link |
---|---|
EP (1) | EP0074755B1 (en) |
JP (1) | JPS5853346A (en) |
AU (1) | AU542894B2 (en) |
BR (1) | BR8205096A (en) |
CA (1) | CA1209784A (en) |
DE (1) | DE3268559D1 (en) |
ES (1) | ES8308242A1 (en) |
ZA (1) | ZA826431B (en) |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2478461A (en) * | 1946-03-16 | 1949-08-09 | Nichols Eng & Res Corp | Apparatus and method for treating foundry sand |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3088183A (en) * | 1960-12-19 | 1963-05-07 | Simpson Herbert Corp | Apparatus for treating granular material |
DE2408981C3 (en) * | 1974-02-25 | 1979-11-08 | Alb. Klein Kg, 5241 Niederfischbach | Process for cleaning bulk materials by centrifugal forces and device for carrying out the process |
GB1463749A (en) * | 1974-08-21 | 1977-02-09 | British Leyland Uk Ltd | Apparatus for use in producing a fluidised bed of granular material |
US3970547A (en) * | 1975-05-22 | 1976-07-20 | Raytheon Company | Air classification apparatus |
GB1493774A (en) * | 1975-05-22 | 1977-11-30 | Raytheon Co | Materials separating apparatus |
DE2921197A1 (en) * | 1979-05-25 | 1980-12-04 | Hermann J Linder | Moulding sand regeneration - in vibrating tank with screens, air sifting, fluidised bed and coolant spiral cooling |
GB2061770A (en) * | 1979-10-27 | 1981-05-20 | Futtans Ltd | Improvements in or relating to the separation of granular mixtures |
-
1982
- 1982-08-30 AU AU87845/82A patent/AU542894B2/en not_active Ceased
- 1982-08-31 BR BR8205096A patent/BR8205096A/en unknown
- 1982-09-01 CA CA000410616A patent/CA1209784A/en not_active Expired
- 1982-09-01 EP EP82304595A patent/EP0074755B1/en not_active Expired
- 1982-09-01 DE DE8282304595T patent/DE3268559D1/en not_active Expired
- 1982-09-02 ES ES515460A patent/ES8308242A1/en not_active Expired
- 1982-09-02 JP JP57153345A patent/JPS5853346A/en active Pending
- 1982-09-02 ZA ZA826431A patent/ZA826431B/en unknown
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2478461A (en) * | 1946-03-16 | 1949-08-09 | Nichols Eng & Res Corp | Apparatus and method for treating foundry sand |
Also Published As
Publication number | Publication date |
---|---|
AU8784582A (en) | 1983-03-10 |
DE3268559D1 (en) | 1986-02-27 |
JPS5853346A (en) | 1983-03-29 |
EP0074755A1 (en) | 1983-03-23 |
ES515460A0 (en) | 1983-08-16 |
BR8205096A (en) | 1983-08-09 |
AU542894B2 (en) | 1985-03-21 |
ZA826431B (en) | 1984-04-25 |
CA1209784A (en) | 1986-08-19 |
ES8308242A1 (en) | 1983-08-16 |
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